Direct lineage reprogramming of mouse fibroblasts to functional midbrain dopaminergic neuronal progenitors

• The first generation of induced dopaminergic neuronal progenitors (iDPs).
• iDPs efficiently generate midbrain dopaminergic neurons.
• Pluripotency factors such as Oct4, Sox2, Klf4 and c-Myc drive the reprogramming.
• SHH and FGF8 specify the fate of the reprogramming.
• Inhibitions of Jak and Gsk3beta highly enhance the conversion efficiency.

The direct lineage reprogramming of somatic cells to other lineages by defined factors has led to innovative cell-fate-change approaches for providing patient-specific cells. Recent reports have demonstrated that four pluripotency factors (Oct4, Sox2, Klf4, and c-Myc) are sufficient to directly reprogram fibroblasts to other specific cells, including induced neural stem cells (iNSCs). Here, we show that mouse fibroblasts can be directly reprogrammed into midbrain dopaminergic neuronal progenitors (DPs) by temporal expression of the pluripotency factors and environment containing sonic hedgehog and fibroblast growth factor 8. Within thirteen days, self-renewing and functional induced DPs (iDPs) were generated. Interestingly, the inhibition of both Jak and Gsk3β notably enhanced the iDP reprogramming efficiency. We confirmed the functionality of the iDPs by showing that the dopaminergic neurons generated from iDPs express midbrain markers, release dopamine, and show typical electrophysiological profiles. Our results demonstrate that the pluripotency factors-mediated direct reprogramming is an invaluable strategy for supplying functional and proliferating iDPs and may be useful for other neural progenitors required for disease modeling and cell therapies for neurodegenerative disorders.